Plasminogen activators may be classified, in accordance with their origins, into tissue activators, vascular activators, blood activators, urokinase, and the like. Plasminogen activators play an important role in fibrinolytic (fibrin-decomposing) activities and are found in a variety of organs of mammalian animals. On the other hand, a great deal of work has recently been made to obtain plasminogen activators from cultured cells. In the above work, there were used as cultured cells, for example, malignant tumor cells, blood vessel endothelium, stimulated macrophage, granular starch cells stimulated by follicle stimulating hormone, and the like. There have also been reported biochemical and immunological properties of plasminogen activators isolated from humoral tissue homogenates, cultured cells and culture media.
However, the purification of human tissue plasminogen activator has seldom been carried out. This is assumably attributed to difficulty in obtaining the starting material in a sufficient amount and, in addition, hydrophobic property of enzymes contained therein, low specific activity, instability of the enzymes in a buffer solution and, in some cases, presence of unknown protease in the course of the purification. Under these circumstances, Rijken et al.) "Biochimica et Biophysica Acta," vol. 580, pps. 140-153 (1979), isolated a human uterus plasminogen activator having a molecular weight of 69,000 and confirmed that the activator is similar both immunologically and biochemically to human vascular plasminogen activator. In addition, another human vascular plasminogen activator having a different molecular weight has also been isolated and identified.
Kwaan et al. [Fed. Proc. 24, 387 (1965)] carried out an investigation on a plasminogen activator derived from human kidney tissue and discovered that the activator is present principally in the endothelium of blood vessels, especially, in the endothelium of artery. It has also been reported by Kucinski et al. [J. Clin. Invest 47, 1238-1253 (1968)], Bernik et al. [J. Clin. Invest 48, 1740-1753 (1969)], Barlow et al. [Thromb. Res. 1, 201-208 (1972)].ANG.sted et al. [Experimentia 33, 589-590 (1978)] and Lewis {Thromb. Haemostas. 42, 895-890 (1970)] that such a plasminagen activator obtained from the cultivation of human kidney tissue is immunologically and physicochemically identical to urokinase.
As a result of an intensive investigation on the tissue plasminogen activator isolated and purified from human kidneys and human blood vessels, the present inventors have made a surprising finding of a plasminogen activator having properties significantly different from those of urokinase derived from human kidneys or human blood vessels, although it has been believed that urokinase is only the principal plasminogen activator available from human kidneys and human blood vessels. The present invention has been completed on the basis of this discovery.